1. Field of the Invention
The present invention relates to increasing the autodecomposition temperature of particular resists. The resists are comprised of structures having recurrent acid labile groups which are typically pendant to the polymeric backbone.
2. Background Art
Processing of semiconductor devices frequently requires the use of temperatures as high as 200.degree. C.; as a result, it is important to have resist structures which can withstand such temperatures without experiencing autodecomposition.
In U.S. Pat. No. 3,779,778, Smith et al. disclosed novel photosolubilizable compositions comprising (1) a water-insoluble compound containing one or more acid-degradable groups, and (2) a photoinitiator comprising a photolyzable acid progenitor.
In U.S. Pat. No. 4,491,628, resists sensitive to UV, electron beam and X-ray radiation capable of forming positive or negative tone patterns upon proper choice of a developer are formulated from a polymer having recurrent pendant groups such as tert-butyl ester or tert-butyl carbonates that undergo efficient acidolysis with concomitant changes in polarity (solubility) together with a photoinitiator which generates acid upon radiolysis. A sensitizer component that alters wavelength sensitivity may also be added. The preferred acid labile pendant groups are tert-butyl esters of carboxylic acids and tert-butyl carbonates of phenols but, it is understood that a wide range of acid labile groups are operative in the invention. These include trityl, benzyl, benzhydryl modifications as well as others well known in the art.
Resists formulated using the preferred tert-butyl esters of carboxylic acids and tert-butyl carbonates of phenols include, for example, poly (tert-butyl vinylbenzoate) (PTBVB) and poly(4-t-butyloxycarbonyloxystyrene) (PTBCS). The autodecomposition temperature (temperature at which the acid labile or photo labile functional group undergoes change or breakdown in the absence of acidolysis or irradiation, respectively) of the PTBVB is about 160.degree. C. as measured by TGA at a heating rate of about 10.degree. C./minute, and the autodecomposition of the PTBCS is about 150.degree. C. at the same heating rate. Thus, there is a need to increase the autodecomposition temperatures if resists formulated from these types of resist materials with acid labile or photo labile pendant groups are to be useful in electronic device processing which may reach temperatures as high as 200.degree. C.